Centralized traffic controlling system for railroads



Nov. 26, 1940.

w. D. HA'lLES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Feb. 25, B38

Flllll k J EQQ 3 Q ATTORNEY INVZFEOR W 55km 2m 3 3% 8 ocfin 1 m m: 0.52 mm :Q Q E 0P mw m Patented Nov. 26, 1940 UNITED STATES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS William D. Hailes, Brighton, N. Y., assignor to General Railway Signal Company, Rochester, N

Application February 25, 1938, Serial No.19 2,575

10 Claims.

This invention relates to centralized trafiic controlling systems for railroads, and more particularly pertains to means for automatically sectionalizing line circuits extending between a control ofiice and a plurality of field stations in a coded centralized traffic controlling system.

In a coded communication system employing a line circuit extending from a control office to several field stations, and including in series electro-responsive means for such stations, it is advantageous to provide sectionalizing means for such circuit at intermediate points in such a manner as to render that portion of the system operative from the control oflice to the most distant station on .the control ofiice side of an abnormally opened condition of the line circuit.

This invention is'to be considered an improvement over the prior application of R. M. Phinney, Ser. No. 145,542, filed May 29, 1937, now Patent No. 2,157,864 granted May 9, 1939, in that a sectionalizing scheme is provided which operates in a positive manner, irrespective of variations in the timing of devices employed at different points.

Another object of this invention is to provide for the automatic restoration to the system of that section of the line circuit rendered inoperative by a break in the control line circuit at any given point as soon as the circuit is again closed at that point.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing the invention in' detail, reference will be made to the accompanying drawing which shows one embodiment of the present invention as applied to line circuits extending between a control ofiice and certain ones of a series of field stations. Similar parts of the system have been designated by similar reference characters, which have been made distinctive by exponents and preceding numerals.

In order to simplify this disclosure, reference is made from time to time to functions common to all parts of a similar character by use of the letter reference characters without exponents or preceding numerals. It isto be understood that such a reference applies to any parts designated in the drawing by reference characters which are similar except for preceding numerals.

For the purpose of facilitating in the explanation and for simplifying the illustration, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and. certain conventional illustrations have been employed, the drawing having been made more with the purpose-of facilitating thedisclosure of the invention as to the principles and mode of operation, than with the idea of illustrating thespecific construction and arrangement of parts that would be employed in practice. the various relays and their contacts are illustrated-in a conventional manner, and symbols are used at times to indicate connections to the terminals of batteries, or other sources of electric current, instead of showing all of the wiring connections to these terminals.

The symbols and are employed-to indicate the positive and negative terminals respectively,.of suitable'batteries, or other source of direct current, and the circuits with which these symbols are used, always have current flowing in the same direction' I In order to simplify the disclosure of this i vention dotted lines have been used toindicate the inclusion of apparatus and circuits. not shown which can be provided in. accordance with the prior art or as typically shown and described in this disclosure.

With reference to the accompanying drawing this invention has been shown as having'been applied to a selector type of communicating system such as is shown, for example, in the Judge et al. Patent No. 2,082,544, dated June 1-, 1937. It is to be understood, however, that the scope of the present invention is not limited to the system shown, and that the present form is used only to facilitate and simplify this disclosure.

In order that the application of the present invention to the above mentioned Judge et al. patent may be readily apparent, reference characters for relays shown in this disclosure have been made to correspond with reference characters provided for relays performing similar functions disclosed in that patent.

The above mentioned communication system provides two-way communication between a'control ofiice (indicated on the left-hand side of the drawing) and a series of field stations. Controls for devices at various field stations are transmitted from the control ofiice to the field stations by means of different series of positive and negative impulses applied'to the line wires l0 and H by the selectiveenergization of relays PC and NC and by the marking off of the'impulses by an impulsing relay EP.

In response to the energization of the control line wires I 0, and H, a biased-to-neutral polarized relay at the control ofii'ce and at each station is positioned, and the positioning of that relay causes the operation of selector means associated therewith. Such selector means, together with the distinctive polarity of, the impulses, provides for the control of several devices at each field station over a single line circuit extending from the control oflice.

The relays SA and SB are neutral relays which are picked up at the beginning of the transmission of a series of impulses, and which remain up throughout that series due to their slow action in dropping away.

.of impulses for the indication cycle.

When a field station has indications to transhot, if the system is at rest, the neutral relay LO at that field station picks up and closes the indication line circuit including line wires A I2 and I3. Relay LO stays up throughout the series It is to be understood that the return line wires H and 13 for the control and indication circuits could as well be combined into a common return wire,'although separate wires have been shown for the purpose of simplifying this disclosure.

1 In the control office the relays MF and MB de tect the-closed condition of the indication line circuit and initiate the transmission over the controlline circuit of a series of impulses for operating the stepping of the selector at the control office in synchronisni with the selector at the fieldv stationwhich is transmitting the indica same batteries could be. used for other purposes such, as furnishing energy for local circuits, and that other suitable sources of energy could as well be used.

, Compensating resistors Rare provided at various points in. order to maintain certain standard conditions throughout the system. Other characteristic features of the present invention are believed to be more clearly understood by considering the mode of operation of the system under various normal and abnormal operating conditions" 1 7 Operation Normal .conditio'ns..Under normal conditions each of the relays D is energized from the battery B at the'most distant field station. Relay D is energized from the positive terminal of battery B through acircuit including line wire l4, back contact E5 of relay SR line wire I 6, resistance R winding of relay D back contact I! of relay S3 line wire l8, winding of relay F back contact IQ of relay SR line wireZl), winding of relay F back contact 2| of relay SB and resistance R to the negative terminal of battery B Relay D is normally energized from the positive terminal of batteryll through a circuit including line wire l4, resistance R winding of relay D back contact 22 of relay SB line wire 20, winding of relay F back-contact 2| of relay SE, and resistance R to the negative terminal of battery B .v

As has heretofore been pointed out, relays D are constructed to operate from a comparatively low voltage, and to operate on a comparatively low current. The characteristics of the relays D are such that the current required for the energize.- tion of all of the relays D in multiple is less than the current required for the energization of the relays F, whereby. the positioning of relays F is uneflected by the energization of the relays D from the field batteries, although the relays F are included in the energizing circuit for those D relays.

Having considered the condition of the system when it is at rest, assume theline circuit to be energized positive from the control ofiice, as would be the case at the beginning of a series of control impulses, conveniently termed a control cycle, in which that polarity is selected for the initiating impulse.

Under such conditions relay PC is picked up and the control line circuit is closed, to position the n relays F, from the positive terminal of battery I B through a circuit including front contact 23 of Hl, winding of relay F backcontact 26 of relay SR line wire l8, winding of relay F back contact I9 of relay SR line wire 20, winding of relay F back contact 2! of relay SE resistance R battery B line wire l4, back contact 5 of relay SR line wire I5, back contact 2! of relay SR line wire H, back contact 23 of relay NC and front contact 29 of relay'PC, to the negative terminal of battery B.

The operation of the polar contacts of the relays F to a right-hand position closes an obvious circuit for energizing relays SA, such circuit having been shown dotted to indicate that a more indirect means of control can be provided, as has been shown in the abovementioned Judge et a1 patent. The picking upof relays SA causes the; energization of relays SB through an obvious circuit, and, due to the slow actingcharacteristics of those relays, they remain in an energized posi: tion throughout the series of impulses, V

The pickingup of relay SE in the conditioning.

period closes a circuit includingwire 38 for shunt ing the battery B out of the line circuit, and the picking up of relays SE andSB causes the dropping away of relays D and D due to thelopening of the circuits for those D relays at backcontacts I! and 22 respectively. After the last impulse in the series has been applied, the dropping of relays F causes the deenergization of the relays SA and SE in turn to mark the end of the series of impulses and to restore the system to the above described condition during a period of. rest. Back-contact 2| of relay S13 when closed, provides energy from battery I? for the energization of therelays D at each field station,

The application of a. negative impulse tothe line circuit at the beginning ofa control cycle due to the picking up of. relay NC causes a similar mode of operation through the same circuits that have beenheretofore described in (12- tail, the battery B being over-powered by the battery B in the control ofilce Which has a much higher "voltage.

Toinitiate an indication cycle,-the relay L0 is picked up at a field station and its energization closes a circuit through its front contact as indicated by dottedlines to energize either of relays MB or MB'to mark the beginning of the condi- Honing period for an indication cycle. After same mode of operation of the system With respect to the control of sectionaiizing devices.

Operation under abnormal conditions.-A line circuit is subject to broken wires at times from a number of sources, such as the weight of ice on the wires, wires broken as a result of fallen trees, land slides, and a number of other conditions. A break in the circuit can also occur at connections from the line circuit to the F relays and other devices. The conditions of the system hereinafter described are to be assumed as resulting from breaks in the circuit due to conditions such, for example, as those mentioned above.

Assume a break to occur in'the line circuit, while the system is at rest, between relays F and F or in that section of the return line represented by wire I6. Under such conditions, relay D is deenergized due to a break in its circuit in either or both of wires [8 and I6, and the dropping away of that relay initiates the picking up of the sectionalizing relay SR through the medium of a time delay means.

Under such conditions the winding of thermal relay THR is energized from through a,

circuit including back contact 3| of relay D back contact 32 of relay SB and winding of thermal relay THR to After thermal relay THR, has completed its operation, a circuit is closed for energizing relay SR from through a circuit including contact 33 of relay THR}, and winding of relay SR to After relay SR picks up, a stick circuit is closed from through a circuit including back contact 3|, of relay D front contact 34 of relay SR and winding of relay SR to The picking up of relay SR closes a loop circuit from relay F in the control oifice including line wire l0, winding of relay F front contact 26 of relay SR compensating'resistor 2R front contact 2! of relay SR and line wire H back to the control office. Thus, it is obvious that conditions are set up whereby relay F can be energized in response to the transmission of impulses from the control office, and that it has a similar mode of operation throughout the series of impulses as has been heretofore described.

Due to the fact that the stick circuit for relay SR is dependent upon backcontact 3| of relay D it is obvious that the line circuit will be maintained sectionalized at that point until the break heretofore described for the energization of that relay during normal conditions.

The picking up of relay D opens the stick circuit for relay SR and causes the closing of back contacts 26 and 21 to again restore the line circuit to normal conditions;

A very similar'mode of operation is employed for the system in case the line circuit is open between relays F and F or in the line return circuit Wire I4. Such a break in the circuit, while the system is at rest, causes the deenergization or relays D and D due to the opening of the circuit for these relays in wire 20 or wire l4, and the dropping away of those relays causes the picking up of relays SR and SR respectively. Relay SR is energized through obvious circuits of which the circuits heretofore described indetail for relay SR are typical.

The picking up of relay SR closes a circuit for energizing relay D from the positive terminal of battery B through a circuit including front contact l5 of relay SR line wire l6, resistance R winding of relay D back contact I! of relay SB line wire l8, winding of relay F front contact l9 of relay SR resistor 3R back contact 35 of relay SB and resistor 2R to the negative terminal of battery B The picking up of relay D under such conditions, opens the circuit for the winding of thermal relay THR to prevent further operation of that relay and also opens the stick circuit for relay SR so as to cause that relay to drop away, pro-' vided that relay should have picked up at the same time or prior to the picking up of relay SR Thus, the line circuit becomes sectionalized so as to render relays F and F responsive to the transmission of impulses from the control office in a similar manner to their energization during the transmission of impulses when the line circuit is closed through all of the F relays.

It is readily apparent that the connection established between front contacts I9 and I5 of relay SR is similar to the connection established at the most distant station in the line circuit and that the circuit is closed through battery B during the period at the beginning of a series of impulses until relay, S13 picks up to close'a shunt circuit around that battery including wire 36.

It is obvious, considering the above example of the operation of the system, that a large number of points of sectionalization can be provided and that the point of sectionalization nearest" the abnormally opened condition of the line circuit, toward the control office, is given superiority for sectionalization over all other points.

Should the line circuit be arnormally opened during the transmission of a series of impulses, the relays F are deenergized, and their deenergization of course causes the restoration tonor mal of other relays associated therewith including relays SA and SB. The dropping away of relays SB under such conditions closes a circuit for allowing the energization of all of the relays D included at stations between the control oflice and the abnormally opened condition of the line circuit, thus effecting the sectionalizing of the control line circuit at the point which will render the system operative between the location of that opened condition and the controloffice.

It is necessary when sectionalizing a control line circuit to also sectionalize the indication line circuit in order to prevent a station beyond the sectionalized point from initiating an indication cycle when the relay LO at that station is picked up. It is necessary to prevent such a condition because the transmission of indications from a field station can be effective only so long as the stepping is provided for the selector means at that station by the transmission of impulses from the control office over the control line circuit. If a station were allowed to initiate the transmission of an indication cycle which could not be completed at that station, the continued registration of a start for an indication cycle by that station would cause undesirable operation of the system. Thus, theindication circuit is opened by the picking up of sectionalizing relay SR at back contacts 3'! and 38, and the indication circuit is also opened when relay SR, is picked up to open the circuit at back contacts 39 and 40. The dropping away of relays SR and SWof course restores'the indication line circuit to normal conditions when the abnormally opened condition in the control line circuit has been closed.

; Although only particular ones of a series of field-stations have been shown and described, it islto be understood that apparatus for other stations can be included in the line circuit between the apparatus which has been shown for the particular stations, and that apparatus at such staitions can provide operation, as shown in the above mentioned prior Judge et a1 patent, without provision for automatic sectionalizing, can provide a manual control switch for sectionalizing the'line circuit or can provide automatic sectionalizing means in accordance with this invention.

Having described automatic sectionalizing means applied to one particular type of communication system as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the -ap-- pending claims.

What I claim is:

1. In a remote control system having a control office and a plurality of field stations, a control relay at the control ofiice and at each of the field stations, a control line circuit serially connecting all of said control relays, a source of energy at the control office, transmitting means at the control ofiice for applying .difierent series of time spaced impulses of current from said office source to said control line circuit, another source of energy at the field station most distant from the control office, means at said most distant field station for energizing said line circuit from said source at that station during the time between successive series of impulses and also during the first impulse of a series but not during the remaining impulses of a series and of insuificient potential to dominate said office source, a detector relay connected across said line circuit at an intermediate field station so as to be responsive to the energization of said line circuit by said another source of energy at said most distant field station between successive series of impulses, and sectionalizing means at said intermediate 'field station responsive to the deenergization of said detector relay for shunting out the line circuit extending away from such intermediate field station towards said most distant field station if said line circuit is deenergized for more than a predetermined period of time between successive series of impulses, whereby an open condition in said line circuit at any .point more remote from said intermediate field st-ationcauses said line circuit to be automatically sectionalized at said intermediate station.

2. In a remote control system, a control ofiice and several field stations, a line circuit including in series electro-responsive means for each of said field stations, a source of energy at said control office, circuit means for energizing said line circuit from said source with different series of impulses, means including a field source'for energizing said line circuit from the most distant field station during the time between each of said series of impulses, a detector relay shunted across said line circuit at certain intermediate stations responsive between said series of impulses only to the energization of that line circuit from said field source at a station more distant from the control ofiice, said field source having a potential sufiicient to energize said detector relays but insufficient to energize said electro-responsive means, means responsive to the deenergization of each of said detector relays for shunting out the section of said line circuit extending beyond that station from said control ofiice, said means for shunting including circuit means for energizing that portion of said line circuit nearest the control office from that station between said series of impulses, circuit means for maintaining said shunting means effective only when said detector relay for that station is deenergized,

cuit shunted out is automatically restored to a portion of the line circuit nearer the control office when the abnormally opened section is closed.

3. In a remote control system, a line circuit connecting a control office and a plurality of field stations, a control line relay connected in series in said line circuit at said control oflice and at each of said field stations, normally inactive transmitting means at the control office for at times energizing said line circuit with different series of positive and negative current impulses from a source of current located at the control ofiice, a detector relay at an intermediate field station connected in multiple across said line circuit on that side of said control line relay at such intermediate station remote from said control ofiice, said detector relay beingof relatively high resistance but requiring a relatively low potential across said line circuit for its operation, means including'a field source at the most remote field station for applying a potential to said line circuit, said potential being of a value sufficient to operate said detector relay but insufficient to operate said control line relays and also insufficient to interfere with the control of said control line relays by said office source of current irrespective of the polarity arrangement of said ofiice source in said line circuit at a particular time, a sectionalizing relay at said intermediate field station, circuit means controlled by said sectionalizing relay when it is energized for opening said line circuit at said intermediate field station between said control line relay at that station and the point at which said detector relay is connected across said line circuit and for shunting said line circuit on the control offi ce side of such opening, and means rendered effective a predetermined time after the deenergization of said detector relay for energizing said sectionalizing relay.

4. In a remote control system including a control oifice, an intermediate field station and a most remote field station, a control line relay at the control ofiice andat each of the field stations. a line circuit connecting said control line relays in series, a normally inactive transmitting means at the control office including a source of current effective when set into operation to energize said line circuit with a control code comprising a at. said intermediate field station, said detector relay being of the high resistance lojwpotential type, m'eansiincluding a field source atsaid most remote field station for applying a potential to said line circuitwof a value sufficient to 'operate said detector relay but insufficient to operatesaid control line relays and also insufiicient to interfere with the control ofv said control line relays by saidoifice source of current irrespective of the polarity arrangement of-said oifice source in said line circuit at a particular -time,..'a sectionalizing relay v at saidintermediate field station, circuit means controlled by said sectionalizing relay when it is-picked up for opening said linecircuit between the control line relay at said intermediate field station and the pointat which said detector relay is connected to said line circuit and for shunting said line circuit on thecontrol office side of such opening, pick-up circuit means rendered eiiective a predetermined time after the deenergization of said detector relay for initially energizing said sectionalizing relay, stick circuit means for said sectionalizing relay for=maintaining'its energization so long as said detector relay is deenergized,-and means controlledby said control line relay at said intermediate field station for disconnecting said detector relay-from said linecircuitand opening said pick-up circuit means for said sectionalizing relay during, each series of impulsesimpressed on said line circuit by said transmitting means.

5. In 'a remotecontrol system, a line circuit connecting a control office and a plurality of field stations, a control line relay connected in series in said line circuit at said control ofiice and at each of said field stations, normally-inactive transmitting means at the control office for at times energizing said'linecircuit with different series of positive and negative impulses from a source of current located at the control ofiice, a detector relay at an intermediate field station connected in multiple across said line circuit 'on the side of said control line relay remote from said control oificeysaid detector relay being of relatively high resistance but requiring a relatively low potential across said line circuit for its operation, means includinga source of current at the most remote field station and governed by saidcontrol line relay atthat station for applying a potential tosaid line circuit during the time between any two series of impulses and for removing said potential during any series of impulses but maintaining the continuity of said line circuit, said potential being of a value sufficient to operate said detector relay but insufiicient to operate said control line relays, a sectionalizing relay at said intermediate field station, circuit means controlled by said detector relay when it is deenergized and by said control line relay at the intermediate field station for initially energizing said sectionalizing relay only if said control line relay is not receiving a series of impulses, circuit means for maintaining said sectionalizing relay energized so long as said detector relay is deenergized, and. circuit means controlled by said sectionalizing relay when it is energized for opening said line circuit between said control line relay at said intermediate field station and the point at which said detector relay is connected and for shunting said line circuit on the control ofiice side of such open condition.

6. In a remote control system, a control office and a plurality of field stations, a control line relay at the control ofiice and at each of the field stations, a line circuit extending between the control o ifice and the field station for connecting all of said controlline relays in series, transmitting means at the control oflice efiective when initiated into operation for transmitting different series of positive and/or negative current impulses over said line circuit, a detector, relay at an intermediate station connected across the line circuit at that station on the side of the control line relay at such station remote from the control office, a sectionalizing relay at said intermediate field station, circuit means controlled by, said sectionalizing relay at said intermediate field station for opening, saidline circuit extending to the more remote field stations, andfor shunting said line circuit, was to render'said control relay at that station energizable from the control ofilce by said transmitting meanasaid opening and shunting of said line circuit, being located betweenthe control line relay for that station-and the point of connection of said detector relay across said linecircuit, means at the most remote field station including a source of energy for energizing said line circuit at a relatively low potential insuificient to operate said control line relays but of a sufficient value to operate said detector relay, circuit means at said intermediate field station responsive to the deenergization of said detector relay forapredetermined time to efiect the initial, energization of said sectionalizing relay and maintaining it energized untilsaid detector relay is again energized, means at saidintermediate field station governed by itscontrol line relay in response to the application of a series of impulses to said line circuit by said transmitting means for disconnecting saiddetector relay from said line circuit and rendering it ineffective to energize said sectionalizing relay, and means at the most remote field station governed-by its control line relay for removing its source orenergy from said line circuit but-effective to maintain the continuity of said line circuit, said-means acting in response to any series of impulses applied to said linecircuit during the operation of said transmitting means at the control office.

7. In a sectionalizingsystem for a series line circuit connecting a control ofiice and a plurality of field stations; apparatus forany given one or more of said field stations for sectionalizing the line circuit. at that station or stations including at each such station a detector relay connected in multiple across said line circuit on the side of a series control line relay at that station more remote from said control oifice; sectionalizing means initially responsive to the deenergization of said detector relay only after a predetermined time and only if the control line relay is not receiving a series of impulses for opening said line circuit between the control line relay at that station and the point at which said detector relay is connected across said line circuit, said means also shunting the control ofiice side of the open point in said line circuit so as to render the control line relay at that station available for energization, said mearis also remaining effective until said detector relay is again energized; means controlled by said control line relayfor rendering said detector relay disconnected from said line circuit and rendering the initial control of said sectionalizing means by said detector relay ineffective; and means controlled by said line relay only if said sectionalizing means at that from said source with different series of impulses,

- stationis effective forv applying a potential to i the control onice side of said line circuit sufficient to operate a. detector relay but insufficient to I operate a control line relay, said means removing said potential during the reception of a series of impulses by said control line relay but also maintaining the continuity of said control line circuit as shunted by said sectionalizing means.

8. In a remote control system, a control oifice 10 and a plurality of field stations, a polarized control line relay at each of the field stations, a line circuit connecting the control ofiice and the several field stations and including said polarized line relaysin series, code transmitting means at the control oflice for transmitting different series of positive and negative impulses over said line circuit, a detector relay at certain of said field stations connected across said line circuit and responsive to a lower potential than said line relays, means at the most-remote field station for applying a potential to said line circuit sufiicient to operate said detector relays but insufiicient 1 to operate said control line relays, sectionallzing meansat each of said certain field stations for opening said line circuiton the remote side of 3 the control line relay at its respective field sta tion and shunting said line circuit to. renderthe line circuit closed on the control ofiice side of I such open condition; means for initially render- 36 ing said sectionalizing means active when said detector relay at its station is deenergized only providing said control line relay at that station is inactive but causing said sectionalizing means r to remain active so long as said detector relay is r 85 deenergized, means at each of-said certain field 4 tionalizing means at that station by'said detector relay, and means at each of said certain field stations for applying a potential to said line cir- 1 cuit on the control ofi'lce'side only if the sectionalizing means at that station is active and only 5 while said control line relayat that station is inactive said potential being sufficient to operate said detector relays but'insuificient to operate said control line relays. v

9. In a remote control system, a control ofi'ice 50 and a plurality of field stations, a line circuit including in series electro-responsive means at said control ofiice and at each of said field stations, a source of energy at said control ofiice,

1 circuit means for energizing said line circuit means including a field source for energizing said line circuit from the field station most distant from said control ofiice during the time between each of said series of impulses, said field source having insufiicient potential to energize said electro-responsive means, a first relay shunted across said line circuit at an intermediate sta tion and responsive to the energization of said line circuit from the field source at said field station between series of impulses and discon-r nected from said line circuit during series of impulses, a second relay responsive to the deenergization of said first relay for a predetermined time only if said first relay is then connected to said line circuit for shunting out the section of said line circuit extending beyond that intermediate station from said control office, whereby an open condition in said line circuit can be detected between said series of impulses and whereby said line circuit .can be automatically sectionalized.

10. In a remote control system, a control ofiice and several field stations, a line circuit including in series a line relay for each of said field stations, circuit means for energizing said line circuit with different series of electrical impulses from an oifice source at said control ofiice, means for energizing said line circuit from a field source at the most distant field station during the time between each of said series of impulses, said field source being of insuificient potential to energize said linerelays, a detector relay connected across said line circuit at an intermediate station responsive to the energization of that. line circuit from the field source at said most distant station between'series of impulses and disconnected from i said line circuit during each series of impulses, a sectionalizing relay responsive to the deenergization of said detector relay for a' p'redeter mined time when said detector relay is not disconnected fromsaid line circuit for shunting out the'portion of said line circuit which extends the other portion of the line circuit when the circuit is again closed at the point of that break. WILLIAM D. HAILES. 

